Objective To investigate the species composition,density and seasonal fluctuations of mosquitoes in Dongcheng District of Beijing from 2020 to 2022,so as to provide a scientific basis for mosquito control.Methods The CO2-light trap was used to monitor mosquito density at 10 monitoring sites from May to October annually during 2020 to 2022 in Dongcheng District.Excel 2007 software was used to organize the monitoring data,GraphPad Prism 5 software was used for statistical analysis,and one-way ANOVA was used to compare the different in groups.Results A total of 7 488 mosquitoes were captured from 2020 to 2022,with the mosquito density of 1.73 mosquitoes per lamp·hour.There was no significant difference in mosquito density in different years(F=1.987,P=0.147 6).Culex pipiens pallens was the dominant mosquito species in Dongcheng District,accounting for 57.71%,followed by Aedes albopictus.The peak mosquito density was occurred in early and late August.The seasonal adult density dynamic of Cx.pipiens pallens and Ae.albopictus was both a single peak curve.Among different environments,the highest density of mosquitoes was in residentials,reaching 2.37 mosquitoes per lamp·hour.There was no significant difference in mosquito density in different habitats(F=1.86,P=0.214 8).Conclusion Dongcheng District should take targeted mosquito comprehensive control measures based on mosquito density,species composition and seasonal fluctuation.Residentials should be highlighted for special attention.It is important to take measures before the peak occurred and prevent the occurrence and spread of mosquito-borne diseases.